Deep-well pump



March 15. 1927.

l. B. WINSOR DEB? wsu. Puur Filed July 24. 1924 INVENTOR Jnnf/'f .5. Mhsar.

ATroRNEY vl B Patented Mar. 15, 1927.

UNITED STATES y 1,621,046 PATENT OFFICE.

IRWIN B. WINSOR, OF LOS ANGELES, CALIFORNIA, ASSIGNOR T0 SINGER Pm 00H- PANY, A CORPORATION 0F DELAWARE.

DEEP-WELL PUMP.

Application led Ju1y24, 1924. Serial No. 728,044.

My invention relates to deep well pumps and pertains more particularly to deep well pumps for pumping oil.

The principal object of the invention is to provide a pump in which slippage is greatly reduced.

Another object of the invention is to provide a pump in which the surface tension and viscosity of crude oil are employed in reducing slippage.

In conformance with other objects, my invention contemplates the use ot a plunger which may be withdrawn through the tubing for inspection, repair or replacement, and it is, therefore, another object of the invention to provide a construction whereby the plunger will readilx7 center itself properly on being returned to the pump barrel.

Another object of the invention is to provide a pump in which metaltometal contact between reciprocating and stationary parts is obviatcd as much as possible, it being my intention to keep a lilm of oil around the plunger at all times as a seal, and it is, therefore, another object to provide for the plunger automatically centering itself with regard to other parts of the pump so that the scaling film is continuous and uniform circumferentially of the plunger.

It will be understood that in oil well pumps-of the more common type the upward stroke of the plunger might be termed both the discharge and suction stroke, while during the downward stroke the oil column is motionless. It is during the upward stroke that the pressure within the plunger between the standing valve and the working valve is negative. It is at this til 1e that the hydrostatic ressure of the oil column, which reaches to tiie surface, acts to force oil back past the clearance of the plunger and into the plunger again. This reverse flow or slippage I propose to overcome by so arranging the parts that the hydrostatic pres- Isure is not transmitted to the `film ot oil immediately surrounding the plunger.

It will bc obvious. particularly hereinafter, that if I prevent return flow or slippage through the plunger clearance, I. will. therefore. reduce the tendency of sand to` be carried into said clearance during the 11p-stroke or ltt of the pump.

It is also a recognized fact that in pumps of the above mentioned type the down-stroke sets up an increased pressure between the two valves. Said increased pressure is due to the fact that the plunger tries to descend more rapidly than the oil can flow upwardly through the working valve. Such back pressure causes a slight leakage upwardly around the plunger, and such flow will act to encourage sand finding its way into the clearance.

It is, therefore, another highly important object of the invention to provide a pressure balancing eti'ect around the plunger so that such slippage is either reduced or eliminated so that sand will be discouraged from entering the clearance immediately surrounding the plunger.

While sand may be kept from the plunger and relatively moving parts, it will, however, tend to settle around the standin valve and it is, therefore, another object o my invention to provide a pump barrel and standing valve construction whereby the act of lifting the standing valve will result in the pump automatically cleansing itself of sand accumulations.

Another object of the invention is to provide a. pump in which the standing valve maybe raised through the tubing.

Another object of the invention is to provide a standing valve assembly which may be effectively anchored down in the pump barrel and in which the hydrostatic ressure of the oil column extending there rom to the surface will act to assist in holding the valve assembly in place during the up-stroke of the plun er.

Still anot er object of my invention is to provide a construction in hollow-plunger, direct-flow single acting pumps which will reduce the possibility of the plunger Working in, or producing, a gas pocket without displacing an oil.

Many ot er objects and advantages of my improved pump will ap ear hereinafter, and they will be better un erstood by virtue of the order of their occurrence hereinafter.

I have illustrated by the accompanying drawings one embodiment ot my invention, and by reference to the drawings and following descri tion of the construction and operation of its parts, those skilled in the art will be enabled to make and use the pump and employ, in this or other embodiments of my invention, or in other pumps, the

scientific principles which I have discovered and ap hed for reducing the slippage and increasing the mechanical etiiciency and life of dee well pumps.

In tlie said drawings,

Figure 1 is a view in vertical section of the lower end of my improved pump;

Figure 2 is a view in vertical section of` the upper end of said pump;

Figure 3 is a view in section seenon a line 3 3 of Figure l;

Figure 4 is a view in section seen on a line 4-4 of Figure 2.

In the pump illustrated, there is provided an e uivalent for the usual hollow plunger in w at I terln the plunger tube 7. Said tube is carried by a reduced end 8 of a plunger head 9. Co-axially of the plunger tube there is provided an outer tube 10 which is carried directly by the plunger head and which is of such internal diameter as to provide an annular space 11 between its inner perimeter and the inner tube. The provision-of the annular space, and the manner in which oil is caused to flow therein, forms one of the salient features of my invention. The plun er head is divided, as at 12, and is provi ed with an annular series of vertical bores 14 which lead from the annular space I1 upwardly and outwardly, as at 15, to points externally of the plun er head. Each of the said bores is provi ed with a seat 16 on which a ball 17 reposes. Pins 18 permit of the balls raising a slight distance only. The plunger head is hollow and screws directly onto a common working' valve cave 19 which is provided with the usual ball 20.

The external diameterof the outer tube is such that it ma pass upward through common tubing suc as 21. The pump includes a larve diameter casing 22 which is incorporated: in the string of tubing by means of special couplings 23 and 24. Coupling 23 is of r duced diameter as at 25 to provide a lead or guide for the lunger when it is being inserted in the casing, although not so shown in the drawing for want of space. Coupling 23 is arranged -at about the samezelevation asthe plunger head when the plunger is in extreme u permost pumping position. In other wor s, when the plunger is raised to the end ofits normal up-stroke, `it is still practically contained within the casing.

In conformance with a salient feature of my invention, coupling 24 is rovided with an'elongated taper seat 27. lipon this seat there normally reposes a-hollow taper plug 28 having a through bore 29 providing a valve seat 30. A ball 3l reposes on the valve seat 30 and said ball and plug co-act to take the lace of the common standing valve. A pm 32 limits the upward movement of the ball. The taper plug is also employed to carry a vertical tube 33 which is hereinafter termed the pump barrel, inasmuch as it serves in the place of the usual pump barrel in eo-action with the plunger to provide for periodically increasing and decreasing the volume existing between the standing valve and the working valve. The pump chamber has no function other than to serve as an enlarged member of a string of tubing so that the space 3l, intermediate of the casing and outer plunger tube, may be subject at all times to the full hydrostatic pressure of the fluid column extending up through the tubing. It should be noted here that an annular area of the plug, indicated by 35, and external to the standing tube 33, is constantly subject to such pressure. Under usual pumping conditions the oil level is well below the surface of the ground and is often only slightly above the pump. Therefore, the force acting to hold the plug upon its seat will be considerably in excess o the pressure acting from below. This pressure difference is depended upon to some extent to hold the plug upon its seat, although it will be apparent that the slight taper of the plug and seat provides for a very effective frictional hold. The metal of the coupling member 24, where the taper bore begins, is beveled as at 3G, to encourage sand gravitating into and through Vthe taper bore when the plug is removed; all for a purpose hereinafter apparent. The lower end ot the inner plunger tube is provided with a valve seat element 36' forced therein. Upon said element a ball 37 rests, the upward movement of which is limited by a pin 38. The ball and seat member act to provide a valve adjacent the extreme lower end of the plunger to increase the effectiveness of the plunger in the presence of gas, as will be explained later.

Inasmuch as some of the objects of the invention are to facilitate removal, repair and replacement of the parts, I will first describe the manner of installing the pump and subsequent`removal of parts for inspection, repair and replacement.

The pump casing and couplings 23 and 21 are incorporated in the string of tubing so that the pump casing may be lowered to the required depth with the tubin f above it acting to provide a fluid course or the oil raised by the pump. The taper plug and standing tube may be installed correctly in the casing before it is lowered, if'desired. After the pump casing and tubing are properly lowered and set the plunger may be sent down through the tubing in the usual manner. The enlarged lower end 10 of the outer tube will guide the plunger and pre- .clude its becoming caught in the joints on the way down. lVhen said end reaches coupling 23 `1t will become centrally loca ted thereby with regard to the standing tube, so

that the outer tube will pass over the standing tube without interference.

For inspection or repairs, the plunger (inner tube` outer tube and plunger head) may be removed through the tubing as a unit without disturbing the tubing. To remove the standing valve. a suitable tool or grab (not shown) is lowered to catch the transverse pin provided in the standing tube. The taper plug may then be jarred loose from its seat and raised, together with the tube. Similarly. it may be returned and driven into place on the seat by droppingr it a suitable distance or by means of jars (not shown), such methods being thoroughly understood by those skilled in the art.

In considering the actual operation ot' the parts in pumping. particular consideration must be given to the fact that a slight clearance exists as at l1 and 43 between the standing tube and the outer and inner plunger tubes, respectively. This clearance I have found may be quite substantial, such as 32 of an inch. In fact, the drawings are quite close to scale as regards the clearances and thicknesses ot the tubes. As the plunger reciprocates the annular' space above the standing tube will increase and decrease accordingly in volume, and such increase'and decrease of volume will result in a certain pumping action through the small valves contained in the plunger head.

In considering the action of the complete pump, let us assume an instance where the pump is at such a depth that the hydrostatic pressure within the pum) casing is 1,000 pounds per square inch, while the fluid level ln the well is such that the pressure in the tubing below the standing valve is 500 pounds per square inch. At the moment of inertia of the plunger, the force Iacting to hold the plug upon its seat will be twice that of the pressure acting from below and a net pressure of 500 pounds per square inch will be acting downwardlyr on said plug. Then the plunger is descending. the net force acting to hold it down will be -evcn greater slightly. lVhen the plunger is moving upward. that area of tbe plug lying within the standing tube will have no appreciable downward pressure. while the pressure from below will be fully effective. The pressure from below, however. may even then be overbalanced b v virtue ot the fact that the annular area of the plug externally of the standing tube is subject to 1.00() pounds per square inch. Proper portioning of the areas mentioned will provide for an excess pressure acting to hold the plug down even during the up-strokc of the plunger. l have avoided mentioning suction in describing the operation of the pump, as it might be misleading. The actual suction effect or suction pressure of this pump during the up-stroke would be the difference bctween the practically negligible pressure above the standing valve and the full pressure ot' the column of fluid which is externaily of the tubing and which acts upwardly from below the pump. In other words, the suction of my pump under the Conditions above assumed would be 500 pounds per `square inch.

Since the pump casing is actually a part of the tubing. the space externally of the plunger and standing tube is subject to the maximum hydrostatic pressure. During the down stroke of the plunger` the pressure within the standing tube and plunger is slightly greater than it is externally of the tubing. Therefore, during the down-stroke there can be no slippage or leakage back into the pump. The conditions existing during the down-stroke will be discussed further hereinafter. it being necessary to first explain conditions during the 11p-stroke of the plunger. Immediately the plunger rises, the space existing between the lowermost plunger valve and the standing valve increases. and the pressure therein of course drops almost instantly to a negligible quantity. It is during the 11p-stroke that` all single-acting hollowplunger pumps leak so badly. In my pump. obviously, oil will tend to rush into the clearance between the outer plunger tube and the standing tube. Such oil does not, however. get into the interior of the standing tube. for the following reasons: As the plunger ascends the annular space above the standing tube increases in volume with the result that oil leaking through the clearance will not build up a back pressure in said annular space, and in spite of such leakage the pressure in the annular space may be less than, and is invariably not appreciabl).r greater than the slight pressure in the standing tube during such 11p-stroke. Therefore. the Oil which leaks into the increasing annular space will stay there as there is little or no pressure difference acting to force it further. The oil which always exists between the inner plunger tube and the standing tube will not escape during the lip-stroke because. as I have just explained1 the pressure in the annular space is then closely approximate to the pressure within the standing tube. Such oil provides a constant seal for the pump.

During the down stroke of the pump. it is obvious and well known that the pressure within the standing tube and plunger will be slightly in excess ot' the maximum pres-- liuull) reach points externally of the plunger. However. during such downstroke the annular space above the standing llltl tube is decreasing. The oil which leaked therein is non displaced upward through the small check valves and outward to the place from which it originally leaked. Such returning oil tends to keep the annular space and the clearances washed of. sand. During the do\vnstroke the upper end of the standing tube may be sald to cO-act with the tuto tubes to provide a small pump, which pumpsthe oil in the annular space back to where it came from and assures the existence of a fluid seal at all times both internally and externally of' the standing tube. lt is a wel] known fact that the flow through a small annular clearance is limited and is very much reduced by any appreciable viscosity such as is peculiar to the heavy constituents of crude oil. During the pumping action of the standing tube and annular space. there is even a tendency for some of the oil which can not travel out through the small,l check valves to travel down between the standing tube and the inner plunger tube.

In fact. it will be apparent that the throttling effect of' the small check valves and the usual throttling efl'ect of the working vulve ma \v be so balanced that the oil seal between the inner tube and the standing tube will remain practically motionless and unchanged during the entire downstroke.

Ity is a very extraordinary characteristic of my pump that during the down-stroke there can be no leakage from the pump casing into the tubes whatever by Way of the clearances, and during the up-stroke there is little or no leakage because of the constant increase of the annularspace above the standing tube.

I do not go so far as to state, as others have done in the art of fluid pumps, that I have obviated slippage entirely. I merely claim to have provided a pump in which the pressure and velocity of the inrushing oil is foiled and arrested in the annular space so that there is not apt to be any sli page into the pump plunger. This arreste slippage is merely forced back where it came from. In other words, I avoid the use of packing. .take advantage of the viscosity ol' the oi] t'or sealing. and take care of any oil that starts to leak into the plunger by pumping it back to where it came from before it can get into the l inne'rtube. Xaturall'v the displacement efficiency of my pump` measuring over the area of the inner plunger tube. will be close to 100 per cent when the valves are tight and the pump is operated at correct speed.

'hile I have shown -and described a specific embodiment of my invention, I do not limit myself to any specific construction or arrangement of parts, and I may alter the construction an( arrangement of parts as I desire or as occasion requires without enlarging the scope of my invention, Within the appended claims.

That is claimed is:

1. In a pump, a single-walled member and a double-walled member relativel reciprocal and providing an internal centra fluid space and an elongated annular space externally coaxial to said fluid space and separated therefrom, a check valve for said single- \valled member, a checkvalve in said doublewalled member at one end of said central fluid space, said double-walled member having discharge passages leading from said central fluid space and said annular space, one of said discharge passages extending through the end of said double-walled member and the other extending laterally through the side of said double-walled member to the exterior thereof.

2. In a pump, a single-walled member and a. double-Walled member relatively reciprocal and providing an internal central fluid space and an elongated annular space externally coaxial to said fluid space and separated therefrom, a check valve for said single-walled member, a check valve in said double-walled member at one end of said central fluid space, said double-walled member having a discharge passage leading from said central fluid space to the exterior of the pump and a discharge passage leading from said annular space to the exterior of the pump, one of said discharge passages extending laterally through the side of said double-Walled member, and a check valve controlling the passage from said annular space.

3. In a pump, a single-Walled member and adouble-walled member relatively reci ro cal and providing an internal central fibid space and an elongated annular space externally coaxial to said fluid space and se arated therefrom, a check-valve for said single-walled member, a check valve in said double-walled member at one end of said central fluid s ace, said double-walled member having a ischarge passage leading from said central fluid space through the end of said double-Walled member and a discharge passage leading outwardly through the side of said doublewalled member, and a check valve in each of said discharge passages.

4. In a pump. a single-walled member and a double-walled mem er relatively reci rocal and providing an internal central uid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening non-return valve for said single-waved member, an upwardlyuopening non-reti rn valve in said double-walled member at one end of said central fluid space, said double-walled memher having a discharge passage leading from the other end of said central fluid space to cal and providing an internal central the exterior of the pump and forming with said central Huid space a fluid course, and a leakage discharge passage leadin from said annular space to the exterior ot the pump at a point remote from the Huid course, said leakage discharge passage and its outlet being entirely isolated from said fluid course, whereby discharge from said leakage discha-r e passage is effected independently of the ow from said fluid course.

5. In a pump, a sinfrle-Walled member and a double-walled member relatively reci rouid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening non-return valve for said single-walled member, an upwardlyopening non-return valve in said doublewalled member at one end of said central fluid space, said double-Walled member having a.discharge passage leading from the other end of said central fluid space to the exterior of the pump and forming with said central fluid space a fluid course, a. leakage discharge passage leading from said annular space to the exterior of the pump at a point remote from the fluid course, said leakage discharge passage and its outlet being entirclv isolated from said fluid course, and a chec charge passagev IRWIN B. WINsoR.

valve controlling said leakage discal and providing an internal central the exterior of the pump and forming with said central fluid space a fluid course, and a leakage discharge passage leading from said annular space to the exterior of the pump at a point remote from the fluid course, said leakage discharge passage and its outlet being entirely isolated from said fluid course, whereby discharge from said leakage discharge passage is effected independently of the flow from said fluid course.

5. In a pump, a sinwle-Walled member and a double-walled member relatively reci rouid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening non-return valve vdiseliaiyge passage and its outlet being entirelv isolated from said fluid course, and a check valve controlling said leakage dis-) charge passage.

IRWIN B. WIN SOR.

DISCLAIMER.

1,621,046.*Irwin B. Winsor, Los Angeles, Calif.

DEEP-WELL PUMP. Patent dated March 15, 1927. Disclaimer filed Februaij 18, 1929, by the assignee by mesne assignments, Joseph G. Richardson. llereby disclaims from claim l of said Letters Patent No. 1,621,046:

ln a pump, a single-walled member and a doublewalled member relatively reciprocal and roviding an internal central Huid space and an elongated annular space external y coaxial to said fluid space and separated therei'rpm, a check valve for said single-walled member, a check valve in said double-v valled member at one end of said central Huid space, said double-walled member having discharge passages leading from said central fluid space and said annular space, one of said discharge passages extending through the end ofsaid double-walled member and the other extending laterally through the side of said double-walled member to the exterior thereof.

And your petitioner disclaims from claim 5 of said Letters Patent No. 1,621,045:

,ln a pump, a single-walled member and a double-walled member relatively reciprocal and providing an internal central fluid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening nonreturn valve for said single-Walled member, an u Wardly-o ening non-return valve in said double-walled member at one end of sai central uid space, said doublewalled member having a discharge passage leading from the other end of said central lluid space to the exterior of the pump and forming with said central Huid space a fluid course, a leakage discharge passa e leadin V-from said annular space to the exterior of the pump at a point remote om the uid course, said leakage discharge passage and its outlet being entirely isolated from said fluid course, and a check valve controlling said leakage discharge passage.

[()jjicicll Gazette March 1.9, 1.929.]

DISCLAIMER.

1,621,046.-Irwin B. Winsor, Los An eles, Calif. DEEP-WELL PUMP. Patent dated March 15, 1927. Disclaimer fi ed April 17, 1929, by the assignee by mesne assignments, Joseph G. Richardson.

Whereas under date of January 31, 1929, your petitioner filed a certain written instrument, [published March 19, 1929, 380 O. G. 494,] wherein and whereby he did disclaim those parts of claims 1 and 5 of said patent and specification which were in said disclaimer set forth and whereas it was intended to disclaim those parts of claims 1 and 4 0f said patent and specification, the intention of filing said disclaimer being to disclaim claim v1 and 4 of said Letters Patent in accordance with the decision of the United States Ilistrict Court for the Southern District of California, holding said claims 1 and 4, invalid:

Now, therefore, for the urpose of carrying out the intention of said original disclaimer and diselaiming c aims 1 and 4 to accord with the findings of such special master in said suit, your petitioner therefore hereby enters this disclaimer to those parts of claims 1 and 4 of said atent and s ecifcation in the following words, to-wit:

Your petitioner hereby disc aims from c aim 1 of said Patent N o. 1,621,046:

In a pump, a single-walled member and a double-walled member relatively reciprocal and provldmg an internal central fluid space and an elongated annular space externally coaxial to said fluid space and separated therefrom, a check valve for said single-walled member, a check valve in said double-walled member at one end of said central fluid s ace, said double-walled member having discharge passages leading from said centra fluid space and said annular s ace, one of said dlscharge passages extending through the end of said double-wal ed member and the other etendfing laterally through the side of said double-walled member to the exterior t ereo And your petitioner disclaims from claim 4 of said Patent No. 1,621,046:

In a pump, a single-walled member and a double-walled member relatively reciprocal and providing an internal central fluid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening nonreturn valve for said single-Walled member, an u wardly-ofpening non-return valve in said double-walled member at one end of sai central uid space, said doublewalled member having a discharge passage leading from the other end of said central fluid space to the exterior of the pump and forming with said central fluid space a fluid course, and a leakage discharge passage leading from said annular space to the exterior of the pump at a pointremote from the fluid course, said leakage discharge passage and its outlet being entirely isolated from said fluid course, whereby discharge from said leakage discharge passage is effected independently of the fiow from said fluid course.

[Qjc'ial Gazette May 7, 1929] DISCLAEMEIFZ.

1,621,046.-^Irw1i B. ll'insor, Los Angeles, Calif. DEEP-WELL PUMP. Patent dat-ed March I5, 1927. Disclaimer filed Februa1 ,l 18, 1929, by the assignee by nielsue assignments, Joseph G. Richardson.

Hereby disclaims from claim 1 of said Letters Patent Nol 1,621,046:

In a pump, a single-walled member and a double-walled member relatively reciprocal and roviding an internal central fluid space and an elongated annular space externally coaxial to said fluid space and separated therefrom, a check valve for said single-walled member, a check valve in said double-walled member at one end of said central fluid space, said double-walled member having disohar e passages leading from said central fluid space and said annular s ace, one of sai discharge passages extending through thc end ofsaid double-wal ed member and the other extending laterally through the side of said double-walled member to the exterior thereof.

And your petitioner disclaims from claim 5 of said Letters Patent N o. 1,621,046:

,In a pump, a single-walled member and a double-walled member relatively reeiproeal and providing an internal central fluid space and au annular space exter ually coaxial to said fluid space and isolated therefrom, an upwardly-opening nonreturn valve for said single-walled member, an u wardly-o ening nonretum valve in said double-walled member at one end of sai central uid space, said doublewalled member having a discharge passage leading from the other end of said central fluid space to the exterior of the pump and formin with said central Huid space a fluid course, a leakage discharge passage leadin `grom said annular space to the exterior of the pump at a point remote from the uid course, said leakage discharge passage and its4 outlet being entirely isolated from said fluid course, and a check valve con trolling said leakage discharge passage." A

[Qpc'ial Gazette March 1.9, 1929.]

DISCLAIMER.

1,621,046.4Irw2`n B. lllmcr, Los ngeles, Calif. Drin-Wma Pmi" Patent dated March 15, 192'?, llisclaimer filed April 17, 192?, by the assigner by mesme assignments, Joseph G. Richardson.

Whereas under date of January 31, 1929, your petitioner filed a certain written instrument, [published March 19, 1929, 380 O. G. 494,] wherein and whereby he did disclaim those parts of claims 1 and 5 0f said patent and specification which were in said disclaimer set forth and whereas it was lntended to disclaim those parts of claims 1 and 4 of said patent and specification, the intention of filing said disclaimer being to disclaim claim 1 and 4 of said Letters Patent in accordance with the decision of the United States istrict Court for the Southern District'of California, holding said claims 1 and 4, invalid:

Now, therefore, for the urpose of carrying out the intention of said original disclaimer and diselaiming c aims 1 and 4 to accord with the ndings of such special master in said suit, your petitioner therefore hereby enters this disclaimer to those parts of claims 1 and 4 of said atent and s ecification in the following words, to-wit:

Your petitioner hereby discliiims from c aim 1 of said Patent N o. 1,621,046:

In 8 pump, a Single-Walled member and a double-walled member relatively reciprocal and providing an internal central Huid space and an elongated annular space externally coaxial to said fluid space and separated therefrom, a check valve for said single-walled member, a check valve in said double-walled member at one end of said central Huid space, said double-walled member having discharge passages leading from said central fluid space and said annular s ace, one of said discharge passages extending through the end of said double-wal ed member and the other elilrtending laterally through the side of said double-walled member to the exterior t ereof.

And your petitioner disclaims from claim 4 of said Patent N o. 1,621,046:

In a pump, a single-Walled member and a double-Walled member relatively reciprocal and providing an internal central fluid space and an annular space externally coaxial to said fluid space and isolated therefrom, an upwardly-opening nonreturn valve for said single-Walled member, an wardly-o ening non-return valve in said double-walled member at one end of said) central dbid space, said doublewalled member having a discharge passage leading from the other end of said central fluid space to the exterior of the pump and forming with said central Huid space a Huid course, and a leakage discharge passage leading from said annular' space to the exterior of the pump at a pointremote from the fluid course, said leakage discharge passage and its outlet being entirely isolated from said fluid course, whereby discharge from said leakage discharge passage is effected independently of the ow from said fluid course.

[Oficial Gazette May 7, 1929] 

